Regulation of cytosolic sodium ion activity in frog sartorius.
To explore the regulation of cytosolic sodium ion activity in the frog sartorius, we used Na(+)-selective microelectrodes to monitor intracellular sodium ion activity in situations of lowering external sodium concentration and elevating external potassium concentration. Reductions of 20%, 40%, 60% and 80% in extracellular sodium concentration produced slight but statistically insignificant changes in the membrane potential of the muscle. However, cytosolic sodium ion activity decreased significantly from 10.0 +/- 1.1 mM to 7.8 +/- 1.1 mM, 7.1 +/- 1.4 mM, 6.5 +/- 1.2 mM and 5.9 +/- 1.1 mM, respectively. In addition, elevation of the external potassium concentration from 2 mM to 12 mM, 32 mM and 62 mM caused respective stepwise depolarization of membrane potential from -87.2 +/- 1.6 mV to -62.4 +/- 3.6 mV, -45.4 +/- 3.0 mV, -27.2 +/- 1.8 mV. Under these conditions, the cytosolic sodium ion activity decreased from 10.5 +/- 1.4 mM to 7.3 +/- 1.6 mM, 6.4 +/- 1.1 mM and 5.2 +/- 0.8 mM, respectively. The results illustrate that the net sodium flux is out of cell either in the reduction of sodium chemical gradient or in the potassium depolarization across the cell membrane.
Yang
J M
JM
Department of Physiology and Biophysics, National Defense Medical Center Taipei, Taiwan, Republic of China.
Yang
S N
SN
D000818:Animals; D002414:Cations, Monovalent; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D008564:Membrane Potentials; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011898:Ranidae; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology
D002414:Cations, Monovalent; D012964:Sodium; D011188:Potassium